The following 851 byte OpenSCAD script will generate a 3D printable drop-in swift link that will convert a mil-spec AR15 to full auto in mere seconds. #3d2a #gunstr

a=1.59;b=5.93;c=10.68;d=13;e=18.67;f=20.26;$fn=64;module c(r,x,y){translate([x,y])circle(r);}module s(h,w,x,y){translate([x,y])square([h,w]);}module e(h,x,y){rotate([x,y])linear_extrude(h){children();}}module P(j,k){polygon([for(i=[j:k])[X[i],Y[i]]]);}X=[0,0,2.76,3.56,3.56,4.35,14.7,15.5,15.5,23-b,23.9,24.34,28.5,29.12,33.95,35.1,39.9,39.3,37,f,37,37,36,34,26.5,18.46,e,f,f];Y=[0,d,d,12.3,4,3.2,3.2,4,c,13.43,17.37,38-f,22.7,23,23,28-b,1.75,.8,.25,0,0,.25,.84,9.46,14.2,12.5,8.6,7,0];difference(){e(12.44){difference(){union(){P(0,19);c(a*2,e,c);}c(a,23.12,18.75);c(2,18.9,10.56);c(6.35,27.82,8);P(20,28);}c(a,e,7);}e(23,-90,0){difference(){s(22.43,d,0,-d);hull(){s(1,1,22,0);c(b,5.3,-6.5);c(b,5.3,-5.81);c(b,17.46,-6.64);}}c(.79,23.1,-21+c);s(a,2.68,22.3,-d);}translate([23.1,0])e(e,0,90)hull(){s(1,1,-d,19.24);s(a*2,1,-12.7,0);c(a,-11.11,18.65);}}

For quite some time I have been writing a remix of the FGC-9 MKII in OpenSCAD to demonstrate that distributing "3D blueprints" is an exercise of free speech, with the goal of fitting the design in a human-readable work of art.

A bit much to fit on a T-shirt, but it should make some nice posters once testing is complete and it is ready to release.